1. Field of the Invention
The present invention relates to image display systems and methods of eliminating mura defects.
2. Description of the Related Art
Each pixel comprises at least one thin film transistor (TFT). To drive the pixel, the corresponding TFT has to be turned on to transmit signals. The brightness of each pixel is dependent on the electronic characteristics of the corresponding TFT. Any deviation during the semiconductor process affects the electronic characteristics of the TFTs, thus, it is unusually for TFTs to have identical electronic characteristics and so different pixels generate different brightness although they are driven by the same gray level. The uneven brightness of the pixels is named mura defect.
One conventional solution to mura defect is to add mura compensation devices into the circuits of the pixels. The mura compensation device can be a voltage driving type or a current driving type. When the mura compensation device is of the voltage driving type, each pixel comprises at least five TFTs and only the mura defects generated by the threshold voltage variations of the TFTs can be eliminated. When the mura compensation device is of the current driving type, each pixel comprises at least four TFTs. When the pixel is driven by low gray level, the performance of the current driving mura compensation device is bad. The mura compensation devices generally require many TFTs. The higher the amount of TFTs required, the lower the aperture ratio, so that the mura compensation devices cannot be applied to display panels with high resolutions, such as 2-inch QVGA systems. The mura compensation devices reduce the brightness of the pixels and enlarge the circuit size of the pixel array.
Another solution to mura defects is external compensation technique, such as that disclosed in U.S. Pat. No. 6,911,781B2, which directly adjusts the gray levels according to reference data. However, U.S. Pat. No. 6,911,781B2 does not disclose techniques of collecting the reference data and does not disclose techniques of adjusting the gray level. Furthermore, U.S. Pat. No. 6,911,781B2 requires a large size for memory to store reference data.
To overcome the defects of the conventional techniques, a novel method for eliminating mura defects is called for, and novel image display systems are disclosed by the invention.